MOUNT_FDESC(8)               System Manager's Manual              MOUNT_FDESC(8)

     mount_fdesc – mount the file-descriptor file system

     mount_fdesc [-o options] fdesc mount_point

     The mount_fdesc command attaches an instance of the per-process file
     descriptor namespace to the global filesystem namespace.  The conventional
     mount point is /dev and the filesystem should be union mounted in order to
     augment, rather than replace, the existing entries in /dev.  This command
     is normally executed by mount(8) at boot time.

     The options are as follows:

     -o      Options are specified with a -o flag followed by a comma separated
             string of options.  See the mount(8) man page for possible options
             and their meanings.

     The contents of the mount point are fd, stderr, stdin, stdout and tty.

     fd is a directory whose contents appear as a list of numbered files which
     correspond to the open files of the process reading the directory.  The
     files /dev/fd/0 through /dev/fd/# refer to file descriptors which can be
     accessed through the file system.  If the file descriptor is open and the
     mode the file is being opened with is a subset of the mode of the existing
     descriptor, the call:

           fd = open("/dev/fd/0", mode);

     and the call:

           fd = fcntl(0, F_DUPFD, 0);

     are equivalent.

     The files /dev/stdin, /dev/stdout and /dev/stderr appear as symlinks to the
     relevant entry in the /dev/fd sub-directory.  Opening them is equivalent to
     the following calls:

           fd = fcntl(STDIN_FILENO,  F_DUPFD, 0);
           fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
           fd = fcntl(STDERR_FILENO, F_DUPFD, 0);

     Flags to the open(2) call other than O_RDONLY, O_WRONLY and O_RDWR are

     The /dev/tty entry is an indirect reference to the current process's
     controlling terminal.  It appears as a named pipe (FIFO) but behaves in
     exactly the same way as the real controlling terminal device.


     mount(2), unmount(2), tty(4), fstab(5), mount(8)

     No ~.  and .. entries appear when listing the contents of the /dev/fd
     directory.  This makes sense in the context of this filesystem, but is
     inconsistent with usual filesystem conventions.  However, it is still
     possible to refer to both ~.  and .. in a pathname.

     This filesystem may not be NFS-exported.

     The mount_fdesc utility first appeared in 4.4BSD.

BSD 4.4                          March 27, 1994                          BSD 4.4